Create assignment, 48975, Exam 3, May 03 at 8:54 pm 1This print-out should have 30 questions.Multiple-choice questions may continue onthe next column or page – find all choicesbefore making your selection. The due time isCentral time.PLEASE remember to bubble in yourname, student ID number, and version num-ber on the scantron!Msci 16 010216:01, general, multiple choice, > 1 min, fixed.001One of the reactions used commercially toproduce hydrogen gas isH2O(g) + CO(g) → H2(g) + CO2(g).A proper expression for the rate of thisreaction could be1. −∆[CO2]∆t.2. −∆[H2]∆t.3. +∆[CO]∆t.4. −∆[H2O]∆t. correctExplanation:The rate of a chemical reaction can eitherbe expressed as the rate of disappearance ofthe reactant (as in this case) or as the rateof the appearance of the product; however,this rate is multiplied by the inverse of thecoefficient of the species in question. Thenegative sign here reminds us that as thereaction progresses, this species is consumedand goes down in concentration.Msci 16 031116:03, general, multiple choice, > 1 min, fixed.002What are the units of the rate constant forthe reaction2 Cl + O2→ Cl2+ O2(M = molarity and s = seconds) rate = k[Cl][O2], where k = rate constant.1. M−2·s−12. M−3·s3. M2·s−14. s−15. M−1·s−1correctExplanation:The unit of rate will always take the formAmount (in mol or concentration)unit timeAs the concentrations are expressed in mo-larity, the rate constant will have units ofM−1·s−1in order for the rate to have units ofM/s.Msci 16 030116:03, general, multiple choice, > 1 min, fixed.003Consider the stoichiometric reaction2 A + B → C + D .The reaction rates are measured with thefollowing results:Initialrate [A]0[B]01 2 12 4 11 2 2The order with respect to [B]0is1. 0 correct2. 13. 1.54. 25. 3Explanation:Create assignment, 48975, Exam 3, May 03 at 8:54 pm 2Since we’re looking at the order of [B]0, allwe have to look at is where [B]0changes andwhere [A]0stays the same. [B]0doubles fromthe first row to the third row, but the ratedoesn’t change, so the rate order is 0.Mlib 05 706516:03, basic, multiple choice, > 1 min, fixed.004Which of the following does not affect the rateof a reaction?1. the value of ∆H correct2. the value of Ea3. the presence of a catalyst4. the temperature of the reactantsExplanation:The presence of a catalyst increases reac-tion rate, as does increasing the temperatureof the reactants. A large Easlows down areaction.Msci 16 041516:04, general, multiple choice, > 1 min, fixed.005Consider the reaction2NOCl(g) → 2NO(g) + Cl2(g)with rate constant 0.0480 M−1· s−1whenconducted at 200◦C. The initial concentrationof NOCl was 0.521 M.What is the concentration of NOCl after0.535 minutes and at 200◦C?1. 0.200 M correct2. 0.289 M3. 0.0239 M4. 0.112 M5. 0.508 MExplanation:k = 0.0480 M−1· s−1[A]0= 0.521 Mt = 0.535 minThe units on k indicates a second orderreaction:1[A]t−1[A]0= a k t1[A]t=1[A]0+ a k t=10.521 M+2 (0.0480 M−1· s−1)× (0.535 min) ×60.0 smin= 5.00 M−1[A]t= 0.200 MMsci 16 040316:04, general, multiple choice, > 1 min, fixed.006The first-order rate constant is k = 3.4 ×10−3s−1for the decomposition of cyclobutane andthe half-life is 204 seconds.cyclobutane → 2(ethylene)What fraction of a sample of cyclobutaneremains after 612 seconds under the specifiedconditions?1. fraction =122. fraction =133. fraction =164. fraction =18correct5. fraction =116Explanation:Create assignment, 48975, Exam 3, May 03 at 8:54 pm 3Make a chart.Time Amount left(cyclobutane=C)0 C204C2408C4612C8After 612 seconds,18of the original amountof cyclobutane is left.Alternate Solution:ln[A]0[A]= a k t= (1)(3.4 × 10−3) sec−1· (612 sec)= 2.08[A]0[A]= e2.08= 8Msci 16 100316:06, general, multiple choice, > 1 min, fixed.007Activation energy for an elementary process1. is the energy required to produce thetransition state from the reactants. correct2. is part of the net enthalpy change for thereaction.3. is smaller for slower reactions and largerfor faster reactions.4. None of theseExplanation:Eareactantsproductstransition stateReaction progressPotential energyWhen the reactants gain enough energy toequal the energy of activation the transitionstate is formed.Msci 16 0908x16:07, general, multiple choice, > 1 min, fixed.008Consider the multistep reaction that has theoverall reaction2 A + 2 B → C + D.What is the rate law expression that wouldcorrespond to the following proposed mecha-nism?A + B → I (fast)I + B → C + X (slow)X + A → D (fast)1. Rate = k[A]2[B]2. Rate = k[I][B]3. Rate = k[A]24. Rate = k[A][I][B]5. Rate = k[A]6. Rate = k[A][B]7. Rate = k[A][B]2correct8. Rate = k[A]2[B]29. Rate = k[B]Explanation:Create assignment, 48975, Exam 3, May 03 at 8:54 pm 4The slowest step is the rate determiningstep and is used to write the rate law.Rate = k[I][B]The rate law must be in terms of reactantsor products so the concentration must notappear in the rate law equation. The stepthat immediately precedes can be treated asan equilibrium system whereRateforward= kf[A][B] = kr[I] = Ratereverseand [I] =kfkr[A][B] can be substituted to givethe equationRate =k0kfkr[A][B]2or Rate = k[A][B]2Msci 16 000416:06, general, multiple choice, > 1 min, fixed.009Consider the potential energy diagramadecbfReaction ProgressPotential Energyfor the one-step reactionX + Y → Z + RThe arrow d represents the1. net change in energy for the reaction.correct2. energy content of products.3. energy content of reactants.4. activation energy for the forward reac-tion.5. activation energy for the reverse reac-tion.Explanation:d is the net change in energy for the reac-tion.Msci 16 100816:08, general, multiple choice, > 1 min, fixed.010Calculate the A in the Arrhenius equation,given that the second order reaction rate con-stant for a reaction is 1.00 ×103L/mol·s at500◦C and the activation energy Eais 19.87kcal/mole.1. 1.00 × 1072. 2.4 × 1063. 1.00 × 1084. 4.55 × 1035. 4.15 × 108correctExplanation:k = 1.0 × 103L · smolEa= 19870calmolT = (500 + 273) K= 773 Kk = A e−Ea/RTA = k eEa/RT=¡1 × 103¢exp£19870(1.987)(773)¤= 4.15 × 108Msci 16 100916:06, general, multiple choice, > 1 min, fixed.011The reactionA + 3 B → C + 2 Dhas a rate constant k = 1.0 × 10−5s−1at27◦C.Create assignment, 48975, Exam 3, May 03 at 8:54 pm 5If the activation energy for the reaction is20,000 cal/mol, what is the value of the rateconstant at 0◦C?1. 3.6 × 10−7correct2. 3.0 × 10−63. 3.3 × 10−54. 2.8 ×
View Full Document
Unlocking...